Effect of natural organic matter on the photo-induced toxicity of titanium dioxide nanoparticles.

Nano-titanium dioxide (TiO2 ) is the most widely used form of nanoparticles in commercial industry and comes in 2 main configurations: rutile and anatase. Rutile TiO2 is used in ultraviolet (UV) screening applications, whereas anatase TiO2 crystals have a surface defect that makes them photoreactive. There are numerous reports in the literature of photo-induced toxicity to aquatic organisms following coexposure to anatase nano-TiO2 and UV. All natural freshwater contains varying amounts of natural organic matter (NOM), which can drive UV attenuation and quench reactive oxygen species (ROS) in aquatic ecosystems. The present research examined how NOM alters the photo-induced toxicity of anatase nano-TiO2 . Daphnia magna neonates were coexposed to NOM and photoexcited anatase nano-TiO2 for 48 h. Natural organic matter concentrations as low as 4 mg/L reduced anatase nano-TiO2 toxicity by nearly 100%. These concentrations of NOM attenuated UV by <10% in the exposure system. However, ROS production measured using a fluorescence assay was significantly reduced in a NOM concentration--dependent manner. Taken together, these data suggest that NOM reduces anatase nano-TiO2 toxicity via an ROS quenching mechanism and not by attenuation of UV. Environ Toxicol Chem 2017;36:1661-1666. © 2016 SETAC.